The present invention relates to electrical coils. It finds particular application in conjunction with water valve actuator coils for ice makers and will be described with particular reference thereto. However, it is to be appreciated that the invention has other applications including actuators for water valves and other appliances, other valve actuators, pull solenoids, other solenoid coils, and the like.
Heretofore, solenoid coils have been utilized to operate water feed valves for home freezer ice makers. To prevent the water supply system from failing with the valve open and flooding the freezer, the actuator coil was designed to burn out and fail when actuated for an excessive duration. The actuator coil was operated at a relatively high wattage such that the current passing through the coil generated a significant amount of heat. As the heat in the coil built, the insulation would start to melt shorting out windings of the coil. The shorting out of some of the windings would reduce the effective resistance of the coil increasing the current flow and generated heat yet more rapidly. A section of the coil wire would rapidly melt under the increasingly higher current and form a break in the electrical circuit. Termination of the current flow eliminated the actuating magnetic flux of the water valve coil allowing the valve to close. In this manner, the inlet water valves for the ice cube makers were designed to burn themselves out if actuated for significantly longer than the fill duration of the ice cube maker.
However, it was also found to be advantageous to connect the water valve actuator coil electrically in series with another resistive load, particularly a heating rod. The heating rod was conventionally actuated to melt the surface of the frozen ice cubes immediately prior to ejection. Although placing the heating rod in series with the valve actuator coil had certain advantages, the series connection changed the failure characteristics of the actuator coil. In particular, the actuator coils no longer burnt out. The coil windings would still heat and start shorting out and reducing the resistance of the coil after the coil had been actuated for an excessive duration. When the coil was connected in series with the resistive load of the heating rod, an effective voltage divider was constructed. The voltage divider limited the amount of power dissipated by the coil. As the coils shorted decreasing the resistance of the coil, more heat was generated by the heating rod and less by the coil. The coil did not burn out.
As the coil shorted out in the series connected coil and the heating rod, the coil was left with too few turns to generate sufficient magnetic flux to open the valve. Accordingly, the actuator coil still failed to maintain the water supply valve open significantly after the normal fill time. However, the coil still continued to conduct current to the heating rod. Thus, even although the water valve failed and closed, electrical current was still applied to the heating rod. Continuous operation of the heating rod converted power into heat at an increasing rate as the windings of the coil shorted out, overheating the ice maker and the freezer. The overheating heating rod would cause the plastic liner of the freezer and other appliance parts to be melted, thus destroying the appliance. Thus, the ice maker was protected from failing into a flood mode at the risk of failing into a mode which caused extensive thermal damage to the freezer or refrigerator.
The present invention provides a new and improved actuator coil which overcomes the above-referenced problems and others. When used in conjunction with a series connected water supply valve actuator coil and heating rod, the present invention protects against both flood damage and excessive heating damage.